Plastic composite deck screw

ABSTRACT

A deck screw for use with plastic and plastic composite deck materials has a shank with a lower segment having a right hand thread and an upper segment having a left hand thread. The upper left hand threaded section has a major diameter which is the same as or slightly less than the major diameter of the lower right hand threaded section. The deck screw evacuates and eject loose material cut out from the deck material as the screw penetrates the deck material, preventing undesirable unsightly deformation of the deck upper surface.

FIELD OF THE INVENTION

The present invention relates to an plastic composite deck screw for use with a powered screwdriver to secure a plastic and composite decking materials to a joist structure.

BACKGROUND OF THE INVENTION

Plastic deck materials, and plastic composite deck materials formed from wood products and other fillers mixed with polymer blends have become popular as an outdoor decking material because they are durable, and because they often replace treated lumber that may be treated with environmentally undesirable chemicals such as arsenic. Composite lumber is an attractive material choice for decking material because it is substantially rot-free. Composite lumber is often fabricated from blends of scrap and/or scrap materials. The materials used include, but are not limited to: plastic bags, plastic jugs (such as those used for milk and water), plastic scraps, wood materials such as sawdust and ground-up wood scraps. Higher quality composite lumber may be constructed of virgin plastics such as polyethylene, polypropylene, and ground-up wood scraps. The use of recycled materials adds to the environmental appeal to the consumer. Examples of such composite decking materials are Trex® (registered trademark of Trex Company, Inc.), Monarch® (registered trademark of John A. Biewer Co., Inc.), and TimberTech® (registered trademark of Timbertech Limited Limited Partnership). Patents disclosing methods of fabrication of such materials include U.S. Pat. Nos. 5,088,910, 5,759,680, 5,851,469 and 6,258,876 which are hereby incorporated by reference. These plastic composite materials are typically formed into decking materials in the form of planks that are attached to a joist structure. The joist structure is usually built from wood, though sometimes the joist structure is built from laminated wood materials or plastic composite materials.

The plastic and plastic composite materials have properties which are different from wood and so typical wood fasteners are not always suitable to attach the plastic or plastic composite decking material to the joist structure. Nails are not very suitable as they may split or crack the decking material. Wood screws can be used but these require pre-drilling of a hole in the decking material and joist before the screw can be used. Generally however, it is too time consuming and uneconomical for a contractor to use ordinary wood screws to fasten decking to joists so this is not typically used.

A “deck screw” is a typical screw used to mount wood deck boards to underlying joists. A deck screw is a threaded fastener with a flat head and shank of uniform diameter to which threading with a steep thread pitch is applied along the lower portion of the shank. Deck screws are typically driven into deck material with a power tool without pre-drilling of a hole. However, these conventional deck screws create problems when used with composite and all-plastic deck materials. This is the problem known as “mushrooming.” The problem of “mushrooming” is best illustrated in FIG. 8, which shows a typical deck screw which has been driven into a plastic composite decking using a power screwdriver. As can be seen, the material of the decking has deformed, leaving a raised ring decking material around the head of the screw. The “mushrooming” effect arises due to the plasticity of the plastic and composite materials which allows the material to deform from the heat created by the friction of the screw fastener as it proceeds into the decking material, combined with the upward pressure caused by the material displaced by the screw threads and body as it enters in the decking material. To provide the proper finished appearance, the “mushroomed” material must be hammered or punched back into the board by use of the appropriate tool. While this sometimes is effective, in other instances the appearance of the hammered-down material is not attractive. Also, striking the deck surface with a hammer may leave the impression of a hammer head on the deck. Using a punch to do the job eliminates the hammer mark problem, but like using a hammer, it is labor intensive.

Furthermore, because decks using plastic or plastic composite decking require more floor joists than decks built from wood, there are a greater number of screws to install. Even a modest deck requires hundreds of deck screws, making each additional step very expensive in terms of added labor.

Several composite decking screw designs have been proposed, including the screw disclosed in U.S. Pat. No. 6,966,737, and U.S. Pat. Nos. 6,666,638 and 6,941,635. U.S. Pat. No. 6,966,737 discloses a screw having two thread sections having different thread pitches and cross-sectional areas, in particular, the shaft of the screw has a cross-sectional area along a cylindrical threaded upper section which is greater than the cross-sectional area along a cylindrical threaded lower section. The disclosed deck screw is designed to capture loose material cut out from the deck material and draw it back into the bore as the screw penetrates the deck material. U.S. Pat. Nos. 6,666,638 and 6,941,635 disclose a deck screw in which an upper threaded section has a major thread diameter which is larger than the lower major thread diameter; and the upper threaded section has a thread angle which is smaller than the lower thread angle. This deck screw is designed to capture and pack loose material cut out from the deck material back into the bore as the screw penetrates the deck material. However, this design is not effective because the packed material gathers at the juncture between the deck board and the joist it is being fastened to. The packed material can prevent proper seating and attachment of the deck board and can force the deck boards of position. The packed material can also cause indentations in the deck board and the joist due to the pressure on the material generated when the board is fastened to the joist.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved plastic composite deck screw for securing a workpiece, such as plastic composite decking, to a base member, such as a floor joist, which avoids the aforementioned problems.

It is an object of the invention to provide an improved plastic composite deck screw which can be used with power tools such as a power screwdriver or screw gun, without predrilling of a pilot hole.

In accordance with one embodiment of the invention, a deck screw for use with plastic and plastic composite deck materials has a shank with a lower segment having a right hand thread and an upper segment having a left hand thread. The upper left hand threaded section has a major diameter which is the same as or slightly less than the major diameter of the lower right hand threaded section. Preferably, the thread angle of the right hand thread of the lower section is less than the thread angle of the left hand thread of the upper section and the thread pitch of the right hand thread of the lower section is greater than the thread pitch of the left hand thread of the upper section. The deck screw evacuates and ejects loose material cut out from the deck material as the screw penetrates the deck material, preventing undesirable unsightly deformation of the deck upper surface.

Other objects, aspects and features of the present invention in addition to those mentioned above will be pointed out in or will be understood from the following detailed description provided in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of an embodiment of a plastic composite deck screw in accordance with an embodiment of the invention;

FIG. 2 is a cross-sectional view of the upper end and head of the plastic composite deck screw of FIG. 1, along the line 2-2 of FIG. 3;

FIG. 3 is a top plan view of the cross-sectional view of the head of the plastic composite deck screw of FIG. 1;

FIG. 4 is a detail view of the area 4-4 of the plastic composite deck screw of FIG. 1;

FIG. 5 is a detail view of the area 5-5 of the plastic composite deck screw of FIG. 1;

FIG. 6 is a front elevation view of the use of the plastic composite deck screw of FIG. 1 as it is driven into a plastic composite board material; and

FIG. 7 is a front elevation view of the plastic composite deck screw of FIG. 6 after being driven into a plastic composite board material.

FIG. 8 is a perspective view of a prior art deck screw after being drilled into a composite board.

DETAILED DESCRIPTION OF THE INVENTION

The plastic composite deck screw of the present invention uses a different design approach than previously used in connection with composite deck screws. Instead of seeking to trap loose material formed during drilling of the screw into composite materials, the screw of the present invention is designed to evacuate and eject loose material cut out from the deck material as the screw drills into and penetrates the deck material. The plastic composite deck screw is provided with a lower section which is threaded with a self-drilling right hand thread which operates in the conventional way to drill into and hold in the materials it is driven into. The plastic composite deck screw is provided with an upper section which is threaded with a left hand thread which evacuates and ejects the loose materials formed by the penetration of the right hand threaded section into the composite material. The evacuation and ejection is accomplished because the upper left hand threaded section has a major diameter, and thus a cross-sectional area, which is the same as or slightly less than the major diameter, and corresponding cross-sectional area, of the lower right hand threaded section. In the preferred embodiment of the invention as shown in the Figures, the major diameter of the threaded upper section is slightly less (no more than 0.10 mm in difference) than the major diameter of the threaded lower section.

In the plastic composite deck screws deck screws of the present invention, the thread angle of the right hand thread of the lower section is less than the thread angle of the left hand thread of the upper section. The thread pitch of the right hand thread of the lower section is greater than the thread pitch of the left hand thread of the upper section.

Referring now to FIGS. 1-7, where like numerals indicate like elements in the drawings, an plastic composite deck screw 10 in accordance with one embodiment of the invention is shown. Plastic composite deck screw 10 comprises a shank 20 and a head 50.

Shank 20 has a lower segment 22 and an upper segment 24. Lower segment 22 is threaded with a right hand thread 26. Upper segment 24 is threaded with a left hand thread 28. Threads 26 and 28 of the lower segment 22 and an upper segment 24 are preferably located adjacent each other without any axial gap between them. Most preferably, threads 26 and 28 are conjoined in a continuous thread pattern as shown at 29 in order to slice away extruded material formed during drilling the screw into a deck material.

The tip end 46 of the shank 20 is preferably provided with a self-drilling tip, most preferably, a Type 17 self-drilling point 48. The self-drilling point preferably has a lead thread 47 at the bottom of the point in order to start self-drilling of the screw when used in harder materials.

The threaded lower segment 22 of the plastic composite deck screw 10 comprises from about 45 percent to about 80 percent of the length of the threaded portions of shank 20, and more preferably, it is between about 60 percent to about 70 percent of the length of the threaded portions of the shank 20. In the most preferred embodiment, the threaded lower segment 22 comprises about two-thirds of the length of the threaded portions of shank 20. The threaded upper segment 24 of the plastic composite deck screw 10 comprises from about 20 percent to about 65 percent of the length of the threaded portions of shank 20, and more preferably, it is between about 30 percent to about 40 percent of the length of the threaded portions of shank 20. In the most preferred embodiment, the threaded upper segment 24 comprises about one-third of the length of the threaded portions of shank 20. Thus for a screw in the range of 70 mm in length, the length of the threaded upper segment 24 will be between 15-17 mm and the length of the threaded lower segment 22 will be between 43-46 mm.

Thread 26 on lower section 22 has a major diameter D₁, thread 28 on upper section 24 has a major diameter D₂. D₂ must never be greater than D₁. D₂ may be equal to D₁, however, the best results are obtained when D₂ is slightly less than D₁. In this application, the definition “slightly less” as used in describing the relationship between D₂ and D₁ means that there is no more than 0.5 mm in difference between D₂ and D₁, and preferably, no more than 0.25 mm in difference between D₂ and D₁, and most preferably, no more than 0.10 mm in difference between D₂ and D₁.

As noted above, the function of the thread 28 is to evacuate and eject the loose materials formed by the penetration of the right hand threaded section into the composite material. The major diameter D₂ of thread 28 is selected to pack as little material as possible. This is in sharp contrast to prior art screws which used the upper thread to pack material into the penetration. Thus the major diameter D₂ of thread 28 should be no larger than the major diameter D₁ of thread 26, and of the same or slightly smaller size. If D₂ is significantly less than D₁ the upper section 24 will not be effective in evacuating and ejecting loose material formed during driving of the screw, so close attention to these tolerances are required.

Referring now particularly to FIGS. 4 and 5, the thread angle A₁ of the right hand thread 26 of the lower section 22 is less than the thread angle A₂ of the left hand thread 28 of the upper section 24. In one preferred embodiment of the invention, the thread angle A₁ of the right hand thread 26 of the lower section 22 is between about 25° to about 40°, most preferably 30°, and the thread angle A₂ of the left hand thread 28 of the upper section 24 is between about 30° to about 45°, most preferably 40°. The use of a higher thread angle A₂ for the left hand thread 28 of the upper section 24 improves the evacuation of material in the area.

Again, with reference to FIGS. 4 and 5, the thread pitch X₁, which is the distance between threads for the right hand thread 26 of the lower section 22 is greater than X₂, which is the distance between threads for the left hand thread 28 of the upper section 24. In the preferred embodiment of the invention, the thread pitch of the right hand thread 26 of the lower section 22 is between about 2.3 mm to about 3.2 mm, most preferably, about 2.8 mm, and the thread pitch of the left hand thread 28 of the upper section 24 is between about 1.8 mm to about 2.8 mm, most preferably about 2.3 mm.

Head 50 of deck screw 10 includes an upper surface 58 having a means for engagement 52 by a fastener driving tool such as a power screwdriver, screw gun, or drill with appropriate bit. The means for engagement 52 can comprise a Robertson square recess as shown in the figures, or a hexagonal recess, a Phillips head recess, a TORX® recess, or it may comprise any other head designs, including straight slot recess, hexagonal head, square head, etc. Head 50 further is provided with an annular channel 54 on the lower surface 56 of head 50 surrounding the shank 20.

The plastic composite deck screw 10 is preferably formed of steel wire by conventional cold forming processes, and it may be anodized or plated as desired with appropriate protective coatings.

The use of plastic composite deck screw 10 is shown in FIGS. 6 and 7. When the plastic composite deck screw 10 is rotated by a power tool, the lower section 22 self-drills into the deck material 62, and continues on into joist 60. In this process, a small amount of deformation 64 is caused in the upper surface of the deck material 62 around the shaft 20 of deck screw 10. As the deck screw 10 continues to drill down, the upper section 24 of the deck screw enters into the deck material 62 and subsequently into the joist 60. Upper section 24 captures and ejects loose material 63 formed by the passage of lower section 22 through deck material 62, releasing the upward pressure causing the deformation 64. As this pressure is relieved, the head of screw 10 is able to be drawn down with counterboring or countersinking into the deck material 62 until the head 50 is seated flush into the board 62, leaving a finished deck material 62 with an upper surface 68 which is not substantially deformed, and an installed deck screw 10 with an upper surface 58 which is substantially flush with the upper surface 68 of the deck material 62. The “mushroom” effect caused by prior art screws which is illustrated in FIG. 8 is eliminated. A small ring 66 of loose material 63 surrounds head 50 and is easily swept away.

The effectiveness of my new deck screw design is the result of a group of elements which work in combination to provide an effective deck screw for use with plastic and plastic composite materials.

It is to be appreciated that the foregoing is illustrative and not limiting of the invention, and that various changes and modifications to the preferred embodiments described above will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention, and it is therefore intended that such changes and modifications be covered by the following claims. 

1. A deck screw for fastening a workpiece to a base member, comprising: a shank having a lower segment having a right hand thread and an upper segment having a left hand thread, said right hand thread of said lower segment having a right hand thread major diameter, said right hand thread and said left hand thread being adjacent each other without a substantial gap therebetween, said left hand thread of said upper segment having a left hand thread major diameter, said left hand thread major diameter being equal to or slightly less than said right hand thread major diameter; and a head having means for engagement by a fastener driving tool.
 2. The deck screw of claim 1 wherein said left hand thread major diameter is slightly less than said right hand thread major diameter.
 3. The deck screw of claim 2 wherein said left hand thread major diameter is 0.10 mm or less smaller than said right hand thread major diameter.
 4. The deck screw of claim 2 wherein said right hand thread of said lower segment and said left hand thread of said upper segment are adjacent each other and provide a length of the threaded portions of the shank, and wherein said right hand thread of said lower segment comprises from about 45 percent to about 80 percent of the length of the threaded portions of the shank.
 5. The deck screw of claim 4 wherein said right hand thread of said lower segment and said left hand thread of said upper segment are adjacent each other and provide a length of the threaded portions of the shank, and wherein said right hand thread of said lower segment comprises from about 60 percent to about 70 percent of the length of the threaded portions of the shank.
 6. The deck screw of claim 4 wherein said screw has a total length of about 70 mm, and said left hand thread of said upper segment has a length of between 15-17 mm, and said right hand thread of said lower segment has a length of the between 43-46 mm.
 7. The deck screw of claim 1 wherein said head has a lower surface with an annular channel surrounding said shank.
 8. The deck screw of claim 1 wherein said left hand thread has a left hand thread angle and the right hand thread has a right hand thread angle, and the left hand thread angle is greater than the right hand thread angle.
 9. The deck screw of claim 8 wherein said left hand thread has a left hand thread angle of between about 30° to about 45° and said right hand thread has a right hand thread angle of between about 25° to about 40°.
 10. The deck screw of claim 8 wherein said left hand thread has a left hand thread angle of about 40° and said right hand thread has a right hand thread angle of about 30°.
 11. The deck screw of claim 1 wherein said left hand thread has a left hand thread pitch and the right hand thread has a right hand thread pitch, and the right hand thread pitch is larger than the right hand thread pitch.
 12. The deck screw of claim 11 wherein said left hand thread pitch has a left hand thread pitch of between about 1.8 mm to about 2.8 mm and said right hand thread has a right hand thread pitch of between about 2.3 mm to about 3.2 mm.
 13. The deck screw of claim 12 wherein said left hand thread pitch has a left hand thread pitch of about 2.3 mm and said right hand thread has a right hand thread pitch of about 2.8 mm.
 14. A deck screw for fastening a workpiece to a base member, comprising: a shank having a lower segment having a right hand thread and an upper segment having a left hand thread, said right hand thread of said lower segment having a right hand thread major diameter, said right hand thread and said left hand thread being positioned to form a continuous thread pattern, said left hand thread of said upper segment having a left hand thread major diameter, said left hand thread major diameter being slightly less than said right hand thread major diameter; said right hand thread of said lower segment and said left hand thread of said upper segment provide a length of the threaded portions of the shank, and wherein said right hand thread of said lower segment comprises from about 45 percent to about 80 percent of the length of the threaded portions of the shank; said left hand thread having a left hand thread pitch and the right hand thread having a right hand thread pitch, said right hand thread pitch being larger than said right hand thread pitch; said left hand thread having a left hand thread angle and the right hand thread having a right hand thread angle, said left hand thread angle being greater than said right hand thread angle; and a head having means for engagement by a fastener driving tool having a lower surface with an annular channel surrounding said shank.
 15. The deck screw of claim 14 wherein said left hand thread major diameter is 0.25 mm or less smaller than said right hand thread major diameter.
 16. The deck screw of claim 15 wherein said left hand thread major diameter is 0.10 mm or less smaller than said right hand thread major diameter.
 17. The deck screw of claim 16 wherein said right hand thread of said lower segment comprises from about 60 percent to about 70 percent of the length of the threaded portions of the shank.
 18. The deck screw of claim 17 wherein said left hand thread pitch has a left hand thread pitch of between about 1.8 mm to about 2.8 mm and said right hand thread has a right hand thread pitch of between about 2.3 mm to about 3.2 mm.
 19. The deck screw of claim 18 wherein said left hand thread pitch has a left hand thread pitch of about 2.3 mm and said right hand thread has a right hand thread pitch of about 2.8 mm.
 20. The deck screw of claim 18 wherein said left hand thread has a left hand thread angle of between about 30° to about 45° and said right hand thread has a right hand thread angle of between about 25° to about 40°.
 21. The deck screw of claim 20 wherein said left hand thread has a left hand thread angle of about 40° and said right hand thread has a right hand thread angle of about 30°.
 22. The deck screw of claim 1 wherein said right hand thread and said left hand thread are positioned to form a continuous thread pattern.
 23. A method of mounting a plastic or plastic composite board to a base member, using a deck screw having a shank having a lower segment having a right hand thread and an upper segment having a left hand thread, said right hand thread of said lower segment having a right hand thread major diameter, said right hand thread and said left hand thread being adjacent each other without a substantial gap therebetween, said left hand thread of said upper segment having a left hand thread major diameter, said left hand thread major diameter being equal to or slightly less than said right hand thread major diameter, said screw having a head having means for engagement by a fastener driving tool, comprising the steps of: engaging said means for engagement with a fastener driving tool; rotating said deck screw in a clockwise direction to drive said deck screw into said board by engagement of said right hand thread of said lower segment with said board and subsequently with said base member, thereby forming loose material in said board, said left hand thread of said upper section evacuating and ejecting at least a portion of said loose material; and said screw head being drawn down into and seated in said board until a screw upper surface is substantially flush with an upper surface of said board and said upper surface of said board is not substantially deformed.
 24. A method of mounting a plastic or plastic composite board to a base member, using a deck screw having a shank having a lower segment having a right hand thread and an upper segment having a left hand thread, said right hand thread of said lower segment having a right hand thread major diameter, said right hand thread and said left hand thread being adjacent each other without a substantial gap therebetween, said left hand thread of said upper segment having a left hand thread major diameter, said left hand thread major diameter being slightly less than said right hand thread major diameter, said deck screw having a head having means for engagement by a fastener driving tool, comprising the steps of: engaging said means for engagement with a fastener driving tool; rotating said deck screw in a clockwise direction to drive said deck screw into said board by engagement of said right hand thread of said lower segment with said board and subsequently with said base member, thereby forming loose material in said board, said left hand thread of said upper section evacuating and ejecting at least a portion of said loose material; and an upper surface of said board being not substantially deformed when said screw is driven into said work member and seated in said board. 